In recent years, high temperature rapid processing has become widespread for the development processing of photographic light-sensitive materials (referred to hereinafter as photosensitive materials) and the processing time for an automatic processor for various types of photosensitive material has been greatly reduced. The achievement of rapid processing requires a developer which provides an adequate density in a short period of time, particularly for a photosensitive material which has excellent development properties; which gives an adequate black density in a short period of time; and which has characteristics such that the material dries quickly after washing with water. Well-known methods to improve the drying properties of photosensitive materials include the pre-addition of an adequate quantity of film hardening agent (e.g., gelatin crosslinking agent) during the coating of the sensitive material; reducing the amount of swelling of the emulsion layer and the surface protecting layer during the course of development, fixation and water washing. Such methods reduce the water content of the sensitive material before the start of the drying process. The drying time is shortened if a large amount of film hardening agent is used in this method, but development is retarded as a result of the reduced amount of swelling, the photographic speed is reduced and gradation is softened, and the covering power is also reduced. Moreover, with high temperature rapid processing with processing agents in which the developer and fixer have essentially no gelatin hardening action, as disclosed, for example, in JP-A-63-144084, the sensitive material must be adequately film-hardened and it is impossible to realize short processing times with silver halide emulsions of which the progress of development is slow. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".) Furthermore, even if the progress of development is improved, the retarded fixing rate, due to high film hardness, leads to problematic residual silver and residual hypo, with residual coloration due to sensitizing dyes, and this impedes any shortening of the processing time. On the other hand, methods in which the development activity of the processing liquids are increased are also known, and sometimes the amount of the main or auxiliary developing agent in the developer is increased, sometimes the developer pH is increased and sometimes the processing temperature is raised. However, all of these methods have disadvantages, such as loss of storage potential of the developer, softening of contrast even though there is an increase in speed, and a tendency to foging for example.
Alternatively, for rapid processing, there is a continued need of improvement in graininess and photographic speeds of such sensitive materials.
Increasing the grain size increases photographic speed but accordingly has an adverse effect on graininess.
Unless high photographic speeds are achieved with grains of the same size (with tabular grains, with the same projected area diameter and thickness), or unless the graininess is improved at the same photographic speed, such improvements are meaningless.
Techniques in which tabular grains are used to provide improvements of the type described above have been disclosed e.g., in U.S. Pat. Nos. 4,439,520 and 4,425,425.
Furthermore, techniques in which the rate of development and the speed/fog ratio are improved by controlling the development initiation points at the corners and/or edges, or in the vicinity of the corners and/or edges, of silver halide grains which have a (111) plane, have been disclosed in JP-A-63-305343 and Japanese Patent Application 62-152330. Moreover, photographic elements for radiographic purposes which have a high covering power by using tabular grains and which do not necessitate a film hardening agent to be added at the time of development by setting the swelling of the hydrophilic colloid layer below 200% have been disclosed in JP-A-58-111933.
As a result of thorough investigation, the inventors have discovered a technique which improves on existing techniques and enables ultra-high speed processing which could not be realized with the existing techniques to be achieved.
Thus, the use of the emulsions with which the rate of development is improved are disclosed in U.S. Pat. Nos. 4,439,520 and 4,425,425 and JP-A-63-305343 could be predicted, but the fact that a post-development drying cannot be carried out in ultra-rapid processing frequently arises. The amount of film hardening agent added was increased on the basis of the technique described in JP-A-58-111933 and preliminary film hardening was carried out so as to provide adequate drying properties in the case of ultra-rapid processing in an automatic processor. Using this sensitive material, the line speed of the automatic processor was increased and, as the dry to dry process speed was increased gradually, the drying properties were maintained at a satisfactory level, but there was a worsening in respect of the residual coloration due to sensitizing dyes; the residual silver; and residual hypo exceeded the permitted limits and fixing failure occurred. Furthermore, there was a pronounced lowering of speed and softening of contrast due to retarded development at this time. There was an improvement in the fixing properties when the preliminary film hardness level was reduced but then problems arose again with regard to drying failure.
On reducing the amounts of gelatin and hydrophilic polymeric material while maintaining the coated silver weight of the sensitive material for maintaining the photographic properties there was a marked worsening in respect of the blackening which occurred when the sensitive material was folded before processing and in respect of the roller marking which occurred where the material was transported by the rollers in an automatic processor, and this was of no practical value.
It has long been known that the fine structure of the silver halide crystals ultimately has an effect on photographic, performance. The following statement is made on page 18 of Photographic Emulsion Chemistry, by Duffin (Focal Press, 1966):
"In the case of a silver iodobromide emulsion, the location of the iodide is the most important factor to be considered. The iodide can be present principally in the interior of the crystals, it can be distributed uniformly throughout the whole grain, or it can be present principally on the outer surface. The actual location of the iodide is determined by the preparative conditions, and its location clearly has an effect on the physical and chemical properties of the crystal."
Silver iodobromide grains are formed with all of the iodide and bromide present in the reactor by introducing an aqueous solution of a silver salt into the reactor. In the so-called single jet method, the silver iodide precipitates first and is easily concentrated in the middle of the grains. On the other hand, with the double jet method in which both iodide and bromide are introduced into the reactor at the same time as the silver salt, the distribution of the silver iodide within the grains can be controlled intentionally. For example, the silver iodide is sometimes distributed uniformly throughout the whole of the grains or, if the addition of the bromide is reduced or stopped during the formation of the grains and the addition of the iodide is continued, it is possible to form silver iodide on the outer surface (the outside) of the grains or to form a silver iodobromide shell which has a high silver iodide content. Silver halide emulsions in which tabular silver iodobromide grains of thickness less than 0.5 .mu.m and diameter at least 0.6 .mu.m, average aspect ratio at least 8, account for at least 50% of the total projected area, in which the said tabular grains have first and second opposing parallel principal surfaces and a central region which extends between the said two principal surfaces, and in which the silver iodide content in the said central region is lower than the silver iodide content in the regions which are displaced transversely in at least one direction spreading to the said two principal surfaces have been disclosed in JP-A-58-113927. Silver halide emulsions in which at least 10% (of the number of grains which are present in the silver halide emulsion) are tabular grains of aspect ratio at least 5 which contain silver iodide in the interior part (corresponding to 80 mol % of the total amount of silver in the grain) inside in the long axis direction or the short axis direction of the grains (an interior high iodide phase), in which the average iodide content of the said interior high iodide phase is at least five times the average iodine content of the silver halide which is present outside the said phase, and in which the silver content of the said internal high iodide phase accounts for not more than 50 mol % of the silver in the whole grain have been disclosed in JP-A-59-99433. Moreover, silver halide photographic emulsions which contain silver halide grains having aspect ratio not more than 5 and having a multi-layer structure, the difference in the average iodine content of two layers which have respective uniform iodine distributions and which are adjacent in the said grains is not more than 10%, and in which the total silver iodide content of the silver halide grains which have the multi-layer structure is not more than 20 mol %, have been disclosed in JP-A-60-147727.
Silver halide photographic emulsions which contain silver halide grains which have a distinct layer structure of which the distinguishing features are that they are comprised of a core part which contains from 10 to 45 mol % of silver iodide and a shell part which contains not more than 5 mol % of silver iodide and that the average silver iodide content is at least 7 mol % have been disclosed in JP-A-60-14331. Moreover, silver halide emulsions of which the distinguishing features are that they have a plural layer structure in which the silver iodide contents differ, that the silver iodide content of the outermost shell is not more than 10 mol %, that a shell which has a silver iodide content at least 6 mol % higher than that of the aforementioned outermost shell is established on the inside of the aforementioned outermost shell, and that an intermediate shell which has a silver iodide content which is between those of the said outermost shell and the aforementioned high silver iodide content shell is established have been disclosed in JP-A-61- 245151. The details disclosed in these patents indicate that better photographic properties can be obtained by changing the silver iodide content in the individual grains according to the location (and especially in terms of the inside and the outside of the grains).
On the other hand, Y. T. Tan and R. C. Baetzold announced at the 41st annual conference of Society of Photographic Science & Engineering that they had calculated the energy states of the silver halides and hypothesized that the iodide in silver iodobromide crystal grains tended to form clusters. The distribution of silver iodide in the tabular silver iodobromide grains described earlier is such that the silver iodide content changes in different portions in units of from 300 to 1000 angstroms, but according to the conjectures of Y. T. Tan and R. C. Baetzold, a more microscopic non-uniform silver iodide distribution is confirmed within the silver iodobromide crystals.
These existing photographic silver halide emulsions were inadequate with respect to photographic speed and their suitability for ultra-rapid processing.